ATtiny85 — 8-Bit AVR Microcontroller in 8-Pin Package

Overview

The ATtiny85 is a famous low-power 8-bit AVR RISC microcontroller IC manufactured by Microchip Technology (Atmel). Housed in an ultra-compact 8-pin DIP package (DIP-8), it is the favored MCU for miniature DIY electronics projects, wearable devices, keychains, and Digispark USB development boards.

Despite its tiny footprint, the ATtiny85 features $8\text{ KB}$ of Flash memory, $512\text{ Bytes}$ of SRAM, $512\text{ Bytes}$ of EEPROM, a 4-channel 10-bit ADC, high-speed 64MHz PWM timer, and an internal $8\text{ MHz} \dots 16\text{ MHz}$ calibrated RC oscillator, allowing operation without any external crystal or supporting components.

Quick reference


CPU Architecture	8-bit AVR RISC
Package	8-pin DIP (ATtiny85-20PU) / 8-pin SOIC / Digispark Module
Max Clock Frequency	$20\text{ MHz}$ (Internal $8\text{ MHz}$ or $16\text{ MHz}$ PLL default)
Memory Breakdown	$8\text{ KB}$ Flash, $512\text{ B}$ SRAM, $512\text{ B}$ EEPROM
Operating Voltage (`VCC`)	2.7 V to 5.5 V DC (1.8 V for ATtiny85V)
GPIO Lines	6 Pins (`PB0` to `PB5`, including `PB5` Reset pin)
PWM & Timers	2 Timers, 4 PWM channels (High-speed 64MHz PLL timer)
Analog Input	4-channel 10-bit ADC (`ADC0` to `ADC3`)
Serial Hardware Interface	USI (Universal Serial Interface for $I^2C$ & SPI)

Pinout (DIP-8 Package)

text

                       ┌───┴───┐
     (PCINT5/RESET) PB5 ─┤ 1   8 ├─ VCC (+2.7V to +5.5V)
    (PCINT3/ADC3)   PB3 ─┤ 2   7 ├─ PB2 (SCK/SCL/ADC1)
    (PCINT4/ADC2)   PB4 ─┤ 3   6 ├─ PB1 (MISO/DO/PWM1)
                    GND ─┤ 4   5 ├─ PB0 (MOSI/SDA/PWM0)
                       └───────┘

Pin	Name	Primary Functions	Arduino Pin Mapping
1	`PB5`	`/RESET`, ADC3, PCINT5	Reset Pin (Pin 5)
2	`PB3`	ADC3, PCINT3, XTAL1	Physical Pin 2 (Analog A3)
3	`PB4`	ADC2, PCINT4, XTAL2, PWM	Physical Pin 3 (Analog A2, PWM)
4	`GND`	Ground Reference (0V)	Ground
5	`PB0`	MOSI, SDA, AREF, PWM0	Digital Pin 0 (PWM / $I^2C$ SDA)
6	`PB1`	MISO, DO, PWM1	Digital Pin 1 (PWM / SPI MISO)
7	`PB2`	SCK, SCL, ADC1	Digital Pin 2 (Analog A1 / $I^2C$ SCL)
8	`VCC`	Positive Supply Input (+2.7V to +5.5V DC)	Power Rail

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{CC}$	2.7	5.0	5.5	V	Standard ATtiny85-20PU
Active Supply Current	$I_{CC}$	—	300	800	µA	$V_{CC} = 3.0\text{V}, f_{CLK} = 1\text{MHz}$
Power-down Current	$I_{pd}$	—	0.1	1.0	µA	$V_{CC} = 3.0\text{V}, T_A = 25^\circ\text{C}$
Internal Calibrated Clock	$f_{RC}$	7.3	8.0	8.7	MHz	Internal RC oscillator
GPIO Output Sink/Source	$I_{IO}$	-40	—	+40	mA	Absolute max per pin

Minimal Circuit (Internal 8MHz Clock - Zero External Parts Needed)

text

        +5V DC Power Supply
           │
        [Pin 8: VCC] ─── [ 0.1µF Capacitor ] ─── GND
           │
        [Pin 1: PB5/RESET] ─── [ 10kΩ Resistor ] ─── +5V
           │
        [Pin 6: PB1] ─── [ 220Ω Resistor ] ─── (LED) ─── GND

Flashing ATtiny85 using Arduino Uno as ISP

Open Arduino IDE $\to$ Examples $\to$ 11.ArduinoISP $\to$ Upload to Arduino Uno.
Install ATTinyCore board package in Arduino IDE.
Select Board: ATtiny25/45/85, Processor: ATtiny85, Clock: Internal 8 MHz.

Arduino Uno (ISP Programmer)	→	ATtiny85 DIP Pin
`5V`		Pin 8 (`VCC`)
`GND`		Pin 4 (`GND`)
`Digital 10`		Pin 1 (`PB5 / RESET`)
`Digital 11`		Pin 5 (`PB0 / MOSI`)
`Digital 12`		Pin 6 (`PB1 / MISO`)
`Digital 13`		Pin 7 (`PB2 / SCK`)

Example (Arduino ATTinyCore Blink Code)

cpp

// On ATtiny85, PB1 corresponds to Arduino Pin 1
const int ledPin = 1; 

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  digitalWrite(ledPin, HIGH);
  delay(1000);
  digitalWrite(ledPin, LOW);
  delay(1000);
}

Common mistakes

Disabling the RESET pin (RSTDISBL fuse): Reprogramming PB5 as a standard GPIO pin via the RSTDISBL fuse permanently disables serial ISP programming. High-Voltage Serial Programming (HVSP) is required to recover the chip.
Forgetting that PB0 and PB1 are used by the Digispark USB bootloader: On Digispark boards, PB3 and PB4 are tied to USB $D+/D-$ pull-up lines.

Notes

ATtiny85 Family: ATtiny25 ( $2\text{KB}$ Flash), ATtiny45 ( $4\text{KB}$ Flash), ATtiny85 ( $8\text{KB}$ Flash).